The present invention generally relates to heating apparatuses and more particularly, to a high-frequency heating apparatus such as an electronic range, an oven range, etc. in which cooking materials of, for example, bread is inserted in a heating vessel loaded in a heating chamber such that processing of the cooking materials from kneading to baking is performed automatically.
An oven range is already commercially available in which processing of cooking materials of bread from kneading to baking is automatically performed in a heating vessel loaded in a heating chamber so as to bake bread. In the known oven range, an annular ring is provided on a bottom of the heating vessel and a mating annular ring engageable with the annular ring of the heating vessel is provided on a bottom wall of the heating chamber in order to position the heating vessel on the bottom wall of the heating chamber. By inserting the heating vessel from above and rotating the heating vessel, the annular ring is brought into engagement with the mating annular ring.
Meanwhile, in the known oven range, a downwardly oriented saw-toothed gear (face gear) is formed at the center of the annular ring on the bottom of the heating vessel and an upwardly oriented mating saw-toothed gear (face gear) engageable with the face gear of the heating vessel is formed at the center of the mating annular ring on the bottom wall of the heating chamber such that power for kneading cooking materials of bread is transmitted through vertical engagement between the face gear and the mating face gear.
However, in the case where a bread is baked by the known oven range, the following problems (1) to (3) arise.
(1) At the time of unloading of the heating vessel from the heating chamber, the heating vessel is required to be displaced upwardly. Thus, if the baked bread is projected out of an upper edge of the heating vessel at this time, an upper portion of the bread will be brought into contact with a top wall of the heating chamber at the time of unloading of the heating vessel from the heating chamber. Hence, in order to obviate such a phenomenon, space in the heating vessel is required to have a large horizontal area. As a result, the obtained bread is flat and small in height.
(2) If misalignment between the face gear and the mating face gear occurs, slip is produced between tooth surfaces of the face gear and those of the mating face gear, thereby resulting in production of noises.
(3) In order to eliminate the above problem (2), fit between the annular ring and the mating annular ring should be made tight. As a result, a large force is required for loading and unloading the heating vessel. Thus, in some cases, a user may inadvertently strike his hand against the wall of the heating chamber, thus resulting in scorch of the hand.
Meanwhile, a high-frequency heating apparatus is known in which a heating vessel incorporating a stirring blade for kneading cooking materials and a turntable for rotating an article to be heated in order to eliminate nonuniform heating of the article are selectively loaded in a heating chamber. It has conventionally been a general practice that in order to eliminate nonuniform heating of the article, the article is placed on the turntable so as to be heated while rotating the turntable. Furthermore, a high-frequency heating apparatus has recently been proposed in which a heating vessel incorporating a stirring blade is loaded in a heating chamber. In this conventional high-frequency heating apparatus, cooking materials of bread, for example, flour, water, sugar, butter, yeast, etc. are kneaded by the stirring blade, fermented and then, baked so as to make bread. One example of such a high-frequency heating apparatus is described with reference to FIGS. 1 and 2. Microwave is introduced from a magnetron 1, through a waveguide 2, into a heating chamber 3. A cylindrical transmission shaft 5 formed integrally with a driven pulley 4 and a drive shaft 6 inserted into the transmission shaft 5 are rotatably mounted on a bottom portion of the heating chamber 3 so as to be projected into the heating chamber 3. Rotation of a high-speed motor 7 is transmitted to the transmission shaft 5 via a belt 9 trained over a motor pulley 8 and the driven pulley 4, while the drive shaft 6 is directly coupled with a low-speed motor 10. A heating vessel 13 and a turntable 14 are selectively loaded in the heating chamber 3 as shown in FIGS. 1 and 2, respectively. A coupling shaft 11 is rotatably mounted on a bottom portion of the heating vessel 13 and a stirring blade 12 is coupled with the coupling shaft 11.
When the heating vessel 13 has been loaded in the heating chamber 3 as shown in FIG. 1, the coupling shaft 11 is brought into engagement with the transmission shaft 5 so as to be coupled with the transmission shaft 5 such that the stirring blade 12 is rotated at a speed of tens to hundreds of revolutions per minute by the high-speed motor 7. Meanwhile, as shown in FIG. 2, the turntable 14 is mounted on an upper portion of the drive shaft 6 so as to be rotated at a speed of several revolutions per minute by the low-speed motor 10.
Thus, the stirring blade 12 and the turntable 14 are, respectively, driven by the different motors 7 and 10 on the following ground. Namely, in the case where dough is made, the stirring blade 12 for kneading materials of bread is required to be rotated at a speed of tens to hundreds of revolutions per minute as described above. Supposing that the turntable 14 is rotated at the above mentioned high speed, an article to be heated on the turntable 14 is scattered and such a great risk may be incurred that a vessel containing the article is broken.
Meanwhile, in recent years, there is a demand for a compact and inexpensive high-frequency heating apparatus which can be operated with ease. However, the conventional high-frequency heating apparatus employs the separate motors 7 and 10 for driving the stirring blade 12 and the turntable 14 and therefore, becomes large in size and expensive, so that the above described demand cannot be satisfied.
A high-frequency heating apparatus is used for selectively heating a dielectric member by dielectric heating of high frequency and is generally used as an electronic range in households. In recent years, the electronic range is very popular as a cooking apparatus for heating various foods in addition to thawing and reheating of frozen foods.
Generally, in the case where bread is made, cooking materials of bread such as flour, butter, sugar, salt, yeast, water, etc. are put into a heating vessel incorporating a stirring blade for kneading the cooking material of bread, kneaded and then, fermented at temperatures of 30.degree. C. to 40.degree. C. Thereafter, heating and baking of the cooking materials of bread are performed at high temperatures. As a result, a long period of about 2 to 4 hours is required for making the bread.
In the case where the electronic oven has such a function that a cooking completion time can be preset such that the bread is baked at the time when the user has waked up, a still longer period is required for completing cooking of the bread after start of cooking of the bread. In cooking of the bread for such a long time, if a door of the electronic oven is kept open through improper operations of the user or mischief of children during heating or during a waiting time after presetting of the cooking completion time, heating may be held in a state of interruption. Meanwhile, even if the door is closed, heating will be held in a state of interruption unless an operation of starting heating is performed.
Meanwhile, even if the user restarts heating after closing the door by noticing that the door is open, fermentation, for example, progresses in the case where the door has been kept open for a long time during a fermentation process, fermentation of the cooking materials is performed excessively. On the other hand, in the case where the door has been kept open for a long time during a baking process, temperature of the bread, which was once raised, drops, such inconveniences are incurred that the bread is baked insufficiently or quality of the finished bread is extremely inferior.
Furthermore, a high-frequency heating apparatus is known in which the heating vessel is made of a heating material for absorbing microwave. In the case where a bread is baked in the conventional high-frequency heating apparatus, cooking materials of bread are initially kneaded in the heating vessel so as to make dough. Subsequently, the dough is fermented in the heating vessel and then, the heating vessel containing the dough is heated by microwave so as to bake a bread.
However, in the conventional high-frequency heating apparatus, since microwave suddenly heats the heating vessel made of the heating material for absorbing microwave, the temperature of the heating vessel is raised sharply. Hence, the surface of the dough, which is held in contact with the heating vessel, is heated to a high temperature, while the temperature of an interior of the dough is not raised so much. Therefore, since there is a large difference in temperature between the surface and interior of the dough, there is such a drawback that the surface of the dough is scorched before the interior of the dough is heated sufficiently.
Meanwhile, a timing belt mechanism shown in FIG. 3 or 4 is used as a power transmission mechanism of a known high-frequency heating apparatus. The timing belt mechanism includes two rotary members spaced a predetermined distance from each other, i.e. a driving pulley 20 and a driven pulley 21, and a timing belt 22. The timing belt 22 is trained over the pulleys 20 and 21 so as to transmit power. Furthermore, an idler pulley 23 acting as an auxiliary rotary member is provided either outside (FIG. 3) or inside (FIG. 4) an intermediate portion of the timing belt 22 in a running direction of the timing belt 22 and depresses the timing belt 22 so as to strain the timing belt 22. The idler roller 23 is rotatably supported by a shaft 24 mounted on a base member (not shown).
In the case where the idler pulley 23 is disposed outside the timing belt 22 as shown in FIG. 3, an angle of winding of the timing belt 22 over the driving pulley 20 can be made larger than that of the arrangement of FIG. 4 in which the idler pulley 23 is disposed inside the timing belt 22, so that efficiency of power transmission can be advantageously improved more than in the arrangement of FIG. 4.
In such arrangements of the timing belt mechanism, not only abnormal noises are produced through contact of the timing belt 22 with the pulleys 20 and 21 and disengagement of the timing belt 22 from the pulleys 20 and 21 at the time of engagement of the timing belt 22 with the pulleys 20 and 21 but the strained timing belt 22 is vibrated through variations of load applied to the timing belt 22 so as to produce vibratory noises. Therefore, the known high-frequency heating apparatus employing such timing belt mechanism has such a drawback that such noises as the abnormal noises and vibratory noises referred to above are produced.